The present invention relates to an ohmic contact to a silicon device and more particularly to a plated ohmic contact in which gold is the first layer on the silicon. The present invention also relates to a reproducible low temperature method of forming a gold-silicon bond.
Ohmic contacts to semiconductor devices must be made from a metal or layers of metal to which thermal or electrical leads can be soldered. However, in order to make a mechanically strong contact, the contact must be strongly bonded to the semiconductor device. A strong bond between metal and semiconductor is commonly achieved by heating the metal until it alloys with the underlying semiconductor.
U.S. Pat. No. 3,711,325 discloses the plating of a silicon device with a thin gold film, then plating a layer of nickel on the gold film. To achieve satisfactory bonding between the gold and the silicon, the composite structure must be sintered at a temperature above 370.degree. C. However, such high temperature may adversely affect other parts of the silicon device, which may have other contacts, e.g. aluminum.
U.S. Pat. No. 3,753,774 discloses a method of making an intermetallic compound. A metal, such as gold, is plated on a semiconductor, such as silicon, and is then sintered at a temperature between 400.degree. and 900.degree. C. Again the drawback of this method is the use of high temperature to achieve satisfactory bonding between the gold and the silicon.